You can fall asleep after an evening coffee and still sleep worse — caffeine quietly trades your deep sleep for lighter sleep.
What the research now says
A 2023 systematic review in Sleep Medicine Reviews pooled 24 studies. On average, caffeine cut total sleep by 45 minutes, lowered sleep efficiency, and shifted sleep toward lighter stages.
Its practical guidance: a normal coffee (~107 mg) should be your last at least 8.8 hours before bed. A strong pre-workout (~217 mg) needs about 13 hours.
Turn that into a cutoff time
- Bed at 11 p.m.? Last coffee by roughly 2 p.m.
- Bed at 10 p.m.? Aim for around 1 p.m.
- Bigger dose or slow metabolism? Push it earlier.
Caffy calculates a personal safe cutoff time from your bedtime and metabolism — and warns you before an afternoon drink eats into tonight's sleep.